It is well known that roadways, runways, and other types of surfaces need to have lines or intermittent stripes painted on them to guide traffic, airplanes, etc. A pavement marking material such as, for example, conventional paint, epoxy, MMA, or thermoplastic (referred to herein generally as “paint”) is used to create visible stripe paint line. Glass beads may be applied to the freshly painted surface immediately after the pavement marking material is applied. The glass beads serve to make the stripes or lines more visible because they reflect light, such as from a vehicle's headlights.
Typically, a flatbed truck is configured to carry all the necessary supplies and equipment so that pavement marking material and beads can be applied to the road surface in an economical fashion. A truck used to apply beads and pavement marking materials, referred to herein as a paint truck, has one or more pavement marking material tanks and one or more bead tank. The bead tank(s) is/are usually large enough to hold sufficient beads for the application to the pavement marking materials in the paint tanks. In some embodiments, different bead tanks may include different types of beads. In operation, paint trucks may travel as fast as 25 mph while painting continuous or intermittent paint lines on the road surface.
Various different systems are utilized to apply paint and can vary based on the type of paint being applied. For instance, “spray,” “extrusion,” and “ribbon gun” are the systems frequently used to apply thermoplastic paints. In these systems the thermoplastic starts out in a solid form, which is heated past its melting point using a furnace mounted on the truck. In alternate arrangements, a separate pumper truck may provide pre-melted materials to a tank of the paint truck. Once the thermoplastic is a liquid material (i.e., melt), the thermoplastic melt is ready for application to a surface. In a spray system, the thermoplastic melt is pumped using a high pressure pump, which pushes the material through a small opening/orifice at the paint gun. This creates a line on the roadway. In the extrusion system, the thermoplastic melt is pumped at a lower pressure and gathers in a collection box disposed by the road surface. The box opens when material is desired and small, flat stream of material is placed on the ground as the vehicle moves forward. The ribbon gun method is similar to extrusion system with the exception of the box used to gather material by the road surface. A ribbon gun places material directly on the roadway after passing through a flat opening as wide as the desired line.
Beads are generally applied using a “pressure pot” system where pressure applied to the holding tank of the beads forces the beads through subsequent connecting lines to an application gun. Glass beads are placed on the paint after the paint gun to help with reflection of the line. Regardless which paint and bead system or combination of systems is used, the equipment for such systems is typically mounted on a flatbed truck.
There is usually a specific amount of paint and beads that one is required to apply per foot to meet various specifications (e.g., state highway requirements). For example, such a specification may require that a 300 lineal feet of a 4 inch wide paint line utilize a gallon of paint and 6 lbs. of beads. Accordingly, it is desirable to monitor the amount of material applied in order to comply with necessary specifications and/or to avoid over application (e.g., waste) of such materials. However, operators often rely on little more than visual inspection, intuition and experience to know how much or how little material they are putting down. For instance, one method commonly used to determine material thickness for thermoplastics is to spray the material onto a flat piece of aluminum and use a micrometer to determine the thickness that the line being applied. This ‘calibration’ information is then utilized to gage application. However, in many instances, such calibration information may change during application.
The volume of paint applied by a spray gun or ribbon gun can change due to a number of different factors. For instance, paint systems typically utilize a number of filters between the gun(s) and the tanks. If the filters accumulate contaminates, the volume of paint supplied to the guns can change. Likewise, in thermoplastic applications the temperature of the thermoplastic melt can affect its viscosity and, therefore, the volume of melt supplied to the paint gun. Further, it is common for the temperature of the melt vary. When such variation occurs, the amount of paint being applied to the roadway may increase or decrease.
Being able to more accurately monitor the amount of paint and/or beads being applied allows the contractor to immediately make adjustments to compensate for such conditions rather than his finding out that he has been applying to little paint to meet specifications for a portion of entirety of a job. Yet another benefit of constantly monitoring paint and/or bead usage would be that the contractor could accurately determine when the supply of paint and/or beads in the tanks on the truck will run out. That is important because in many situations the tanks on the painting truck can not readily be refilled. For example, on interstate highways, safety regulations prohibit filling the paint and or bead tanks on paint trucks on the interstate highway. The paint truck must exit the interstate prior to refilling its tanks. If a contractor knows that the paint and/or bead supply is running low, he or she can exit the interstate at a convenient time prior to running out of paint and/or beads. If the contractor runs out he has to drive to the next exit, get refilled, then backtrack far enough to get back to the point where he ran out. This results in a waste of time. The problem of such inefficiencies—and how they are magnified—becomes clear when one appreciates that a paint truck must always operate with several other traffic control vehicles. So it is not one, but several vehicles which must backtrack in these circumstances.
Beyond experience and intuition, certain devices and methods exist in the prior art for monitoring the amount of materials being used. For both beads and paint tanks, one can measure the amount of materials used to refill the tanks. Whatever volume of materials was used is then divided into the number of lineal feet painted since the last refilling stop to determine material usage. Another method entails the use of flow meters, which can be placed in the lines connecting the paint tanks to the discharge nozzles.
In the case of thermoplastic there are obstacles that have prevented the use of flow meters. First, thermoplastic melts are heated beyond the operation range of flow meters. A second problem is the abrasive nature of the material. Flow meters that operate by inserting some kind a paddle wheel into the path of the material flow will quickly cease to work because the material will simply eat away the paddle wheel as it flows past due to friction. Other non-intrusive flow meters may also not work in such an environment. Certain non-intrusive flow meters rely on bouncing electronic signals back and forth from one side of a pipe to the other. These signals are can then determine the flow through the pipe. However, thermoplastic can contains glass beads within its melt, these glass beads scatter the electronic signal and make it impossible to measure flow.